Electrical contacting device



Filed July 7. 1951 III v Q T U a m H W v F N L M. W 0 Z w w m M Y U B C Hill ATTORNEYS United States Patent O 2,742,543 ELECTRICAL CONTACTING DEVICE Clifford w. Hurd, Piedmont, Calif. ApplicationJuly 7, 1951, Serial No. 235,618 Claims] Cl; 200-67) This invention relates to improvements in electrical contacting devices, and more particularly to an improved snap action switch operable in response to relatively minor thermostatically controlled forces to cause a very rapid or snap-acting opening and closing movement of movable electrical contacts in relation to fixed electrical contacts.

The principal object of the invention is to provide an improved snap action switch of that general type exemplified in the patents to Hanel 1,848,171 and Kercher 2,314,989 to the end that the switch will embody actuating means and control means therefor enabling a more rapid snap action and a wider range of operation with respect to variance in the magnitude of forces which may be available for switch actuation.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the drawing forming part of this specification, and in which:

Fig. l is a view in side elevation of the thermostatically controlled switch embodying the present invention;

Fig. 2 is a top plan view of the switch of Fig. 1;

Fig. 3 is a view in section taken along lines 3-3 of Fig. l;

Fig. 4 is a view in section taken along lines 44 of Fig. 2;

Fig. 5 is a view in section, somewhat enlarged, taken along lines 5-5 of Fig. 2; and V Fig. 6 is a view in section, also somewhat enlarged, taken along lines 6-6 of Fig. 2.

Referring to the drawing, the switch comprises spaced mounting plates 10 and 12 connected together, as by a plurality of posts 14 having flange connections 16 with the underside of plate 10 and connections with plate 12 constituted by bolts 18 having a threaded. engagement with the interiors of posts 14. The plate 10 is secured to an adapter 20 carrying a union nut 22 which is threadably engaged with a length of pipe or tube 24 which is adapted to be secured, by means not shown, to a fixed support.

Posts 26 and 28, constituting the terminals of an electrical circuit, not shown, to be controlled by the switch, are mounted on plate 12. Terminal posts 26 and 28 are connectable together through the following preferred arrangementz'lead 30, connected to post 26 and constituting one end of a resistance coil 32 mounted on mandrel 34 clamped between mounting arms 36 by bolt 38 and nut 48; lead 42, constituting the other end of coil 32, extending between the head of bolt 38 and an arm 36; the latter extending through plate. 12 and terminating in inturnedrfeet 44; plate 46 "clampedto the underside of plate 12 by feet 44; fixed silver contact 48'secured to plate 46; movable silver contact 50; flexible lead 52, preferably of woven or braided wire ribbon, secured at one end, as by silver brazing or soldering, to the underside of contact 50 and secured at the other end, as by brazing, between a copper disc 54 and the head of a copper rivet 56; rivet 56, extending through bushing 58 in plate 12 and securing arm 60 to said plate; and arm 60 to terminal 28. The

2,742,543 Patented Apr. 17, 1956 2 underside of the lower end of lead 52 is brazed to the upper end of copper rivet 62 which has sleeved thereon a blowout plate 64 and three insulating washers 66, 68 and 70 of varied diameter.

A control connection for the movable contact assembly comprises a strip 72 of spring metal, such as beryllium copper, said strip being fixed at one end to a pin 74 journalled for free pivotal movement in apertures 76 of lever arms 78 and having at its other end a bifurcated portion 80 extending between washers 66 and 70 in embracing relation to washer 68. Strip 72v is thus provided with a free connection in a longitudinal direction with the movable contact assembly, but washers 66 and 70 constrain the end of the strip against relative movement vertically with respect to the contact assembly. An integral tongue 82 is formed in the strip 72 and said tongue is provided with a knife-edge end engaging with a notch 84 in an abutment member 86, said member being sleeved on the adapter member 22 and extending upwardly through plate 10.

Lever arms 78 have a free pivotal connection with plate 10, the arms being provided with notches 88 and the plate with notches 90 for this purpose. The arms 78 are provided at their upper ends with apertures 92 serving as the journal supports for the ends of a pin 94. Guide rods 96 have corresponding ends extending through apertures in pin 94, with the other ends of said rods extending into sockets formed in the head portions 98 of bolts 100, said bolts extending through plates 10 and 12 and bushings 102 and being secured in place by nuts 104. Compression springs 106 are mounted on the guide rods between the pin 94 and adjustment nuts 108 which are threadably engaged with the rods.

A temperature responsive control system for the adjustable snap action switch described may consist of temperature sensitive elements such as tube 24 and cylinder 110, said elements having a relatively high coefficient of thermal expansion, and rods 112, one on each side of elements 24 and 110, having a low coefficient of thermal expansion. The lower ends of rods 112 are interconnected by crossbar 114 fixedly secured to the underside of cylinder and the upper ends of the rods are interconnected by crossbar 116, as by nuts 118 threadably engaged with said rod ends. An externally threaded stud 120 is threadably engaged with the bar 116 at the center thereof, and locknut 122 carried by stud 120 enables the locking of the stud with respect to the bar after the stud has been desirably adjusted vertically with respect to push button 124 afiixed to spring strip 72. Stud 120 extends through aperture 126 in plate 12 to engage the button 124.

In operation, the switch may be used to control the circuit containing a heating element for a medium which is in heat transfer relation to the temperature sensitive elements 24,110 and 112. For example, the described switch is particularly useful and desirable for the control of flash steam boilers where the operating temperatures are substantially higher than the temperatures at which switches of this general type have been heretofore used. It will be appreciated that the greater the operating temperature is of the unit controlled by such switchesthe greater the force must be that urges the tongue 82 against the abutment member 86. In the subject switch the means employed to control the longitudinal tensioning of strip 72, and therefore the force which tongue 82 exerts against the abutment member enables an extremely wide range of control as well as a many-fold multiplication of tensioning forces.

The positions of nuts 108 on rods 96 determine the tensioning force. The force exerted by the compression springs on nuts 108 and pin 94 tends to rock the lever arms in a counterclockwise direction (Fig. 6) about their points of free pivotal connection with plate 10 and this force ismultipli'edby' "the 'le'veraims' and t'ran'sriiit'ted' as a tensioning force to strip 72. The spring force is multiplied a number oftimes equal to the ratio of the distance between the'pivot ala'xis' of the arms and the pivotal axis of 'pin' 94 'to thedistarice between the former'axis and the point ofconnection between strip 72 and pin 74. The

tongue 82, being normally located-below the-plane occupied"by"the' balance of strip 72, biases the movable contact assembly to closed position. J

As the temperature sensitive elements 24, 110 and 112 are heated to a temperature at which it is desired, as evid'enced by the respective adjustments of nuts 108 and stud 120, that contact between the fixed contact48 and-movable contact 50 'bebroiien,the relative thermal movement between elements 24 and 110 and rods 112 will move thes'tu'd120 downwardly to depress'the strip 72 and move the same into a co-planar position with tongue 82, whereupon a minute degree of further downward movement will movethe strip beyond this dead center position arid tongue 82 will cause the free end of strip 72 to' be's'napped downwardly to bring contact 50 out of engagement with contact 48.

As the temperature-elements cool to a point where it isdesired, as evidenced bythe spring and stud adjustments, that the contacts here-engaged, stud=120 will be moved ment member at a point at which the tongue will extend above the strip, in which position the movable contact 50 will be out of engagement with the fixed contact, and to provide an actuating element for the strip which acts to positively move the same upwardly, rather than, as is the case with stud 120, downwardly.

From the foregoing it will be seen that I have provided an improved electrical contacting device in the form of the snap acting switch described, and while a single and preferred embodiment of the same has been disclosed it is to be understood that all substantial equivalents of said embodiment are within the scope of the invention.

What is claimed is: a

1. In an electrical contacting device having a fixed contact, and a movable contact carried for vertical movement toward and away from said fixed contact by one end of a substantially horizontal resilient strip, said strip being supported at its other end and having a tongue portion struck therefrom, with said tongue portion being directed toward the supported end of the strip and engaging a fixed abutment member, whereby a moving force applied substantially normal to said strip between the supported end thereof and said tongue will cause an abrupt movement of said movable contact with respect to said fixed contact; the provision of a substantially vertical lever arm having a fulcrum located ata level beneath the supported end of said strip, a pivotal connection between said lever and the supported end of said strip, and compression means disposed above said strip in forcing engagement with the upper end of said lever tending to rock said lever arm about its fulcrum in a direction to apply a longitudinal tensioning force to said strip.

2. In an electrical contacting device having a fixed contact, and a movable contact carried for vertical movement toward and away from said fixed contact by one end of a substantially horizontal resilient 's'trip, said "strip being supported at its other endand having a tongue portion struck therefrom, with said tongue portion being directed toward the supported end of the strip and engaging a fixed abutment member, whereby a moving force applied substantially normal to said strip between the supported end thereof and said tongue 'will cause an abrupt movement of said-movable contact with respect to'said fixed contact; the provision of a substantially vertical lever arm having a fulcrum "located at a'-levelbeneath the supported end of said strip, a pivotal supporting connection between said lever and the supported end of said strip, and means in forcing engagementwith the upper end of said lever tending to rock said lever arm about its fulcrum in a direction to apply a longitudinal tensioning force to said strip, said means comprising a guide rod in substantial parallelism with said strip, a slidable connection between said lever arm and 'endof said rod, a spring sleeved on said rod and maintainedin compression thereon between said arm and'a' member carried by-the rod, and a fixed socket member anchoring the other end of said rod.

3. In anel'ectrical contacting device as set forth in claim 2, said'member 'con'sisting'of a nut threadably engaged with said rod and adjustable thereon to vary the force exerted by said sp'ring'on 'said lever arm.

4. An electrical contacting device comprising a fiat strip of spring metal, pivotally mounted means including a rockable lever arm and means constituting a fulcrum support for said arm pivotally supporting one end of said strip, a tongue struck'from said strip and extending toward said lever arm, fixed abutment means in engagement with the end of said tongue adapted to normally maintain said tongue slightly out of the plane-of said strip, and yielding means disposed in reactingrelation 'to said lever arm tending to rock said arm and thereby cause said arm to exert a pulling force along the longitudinal axis of said strip.

5 An electrical contacting device comprising a fiat strip of spring metal, a support member, an arm having a pivotal'conr'iec'tion with said member, a pivotal connectionbe'tween said arm and one end of said strip, the

pivotal axes of said connections beingparallel and in spaced relation, compression means supported by said member in reacting relation to said arm and adapted to impart a' rotative force to said arm to urge a longitudinal movement of said strip in a direction in which said one end of said strip would be the leading end, fixed abutment means, and means integral' with said strip extending in the direction of said one end of said strip in a normally non-coplanarpa'th with respect to the body of said strip and engaging said abutment means, said latter means biasing said other end'of said strip in a direction transverse to the longitudinal axisofsaid strip in opposition to the longitudinalforceapplied to said-strip.

References Cited in the file of this patent UNITED STATES PATENTS 2,077,362 Holm Apr. 13, 1937 2,198,428 Turner-etal. Apr. 23, 1940 2,314,989 Kercher Mar. 30, 1943 2,528,756 Kaser Nov. 7, 1950 2,541,370 Koonz et a1 Feb. 13, 1951 2,573,588 Miller on. 30, 1951 FOREIGN "PATENTS 603,535 Great Britain June 18, 1948 688,913 'Great Britain Mar. 18, 1953 

